1. Field of the Invention
The present invention relates to flat panel displaying technology, and in particular to a laser frequency adjustment method and a laser frequency adjustment system.
2. The Related Arts
The displaying technology has been undergone fast development recently. A flat panel display device is significantly different from a traditional video image displaying device by adopting totally different displaying and manufacturing technology. The traditional video image displaying device is generally based on a cathode ray tube (CRT), from which a flat panel display device differs primarily concerning changes made in respect of weight and size (thickness). Generally, a flat panel display device has a thickness not greater than 10 centimeters, among the other differences associated with various technical aspects, such as theory of displaying, manufacturing material, manufacturing process, driving for displaying video images.
The flat panel display device possesses features such as being completely flattened, being light and thin, and energy saving and currently undergoes progresses toward high PPI (pixels per inch), low power consumption, and high integration. Amorphous silicon, which is conventionally used, due to inherent limitation, cannot suit the above described needs and poly-silicon is considered the best candidate for substituting amorphous silicon for poly-silicon is fit for the needs for future developments of the flat panel display device.
As links of the technical cores of the low temperature poly-silicon displaying technology, the manufacturing process and material behavior of poly-silicon determine the performance of a display device. The manufacturing processes of poly-silicon that are currently known include: low pressure chemical vapor deposition (LPCVD), solid phase crystallization, metal induction, and laser annealing. The most commonly used process in the industry is the laser annealing operation, which uses the high temperature generated by a laser beam to melt amorphous silicon for re-crystallization to form poly-silicon. Although adjusting parameters of the laser beam may better the result of crystallization, due to limitation imposed by the specifications of operation machines, parameters and the ranges thereof that can be modulated are limited, such as laser frequency, so that it is impossible to conduct more thorough study of the process of crystallization of poly-silicon and the result thereof.
As shown in FIG. 1, which is a schematic view showing an optical path of a laser pulse used in a prior-art laser annealing process, in the drawing, a primitive laser pulse 100 passes through a beam splitter 200 so that the primitive laser pulse 100 is split into two sub-laser pulses 101, 102. The energy of each of the sub-laser pulses 101, 102 is 50% of that of the primitive laser pulse 100. The sub-laser pulse 101 is subjected to reflection by four reflectors 300 to transmit back to the beam splitter 200 to be superimposed with the sub-laser pulse 102. Since the sub-laser pulses 101, 102, after passing through the beam splitter 200, shows a down-shifting distance in the vertical direction, a compensator sheet 400 is used to adjust the superimposed laser pulse 103 back to the original vertical position. During such a process, compared to the sub-laser pulse 102, the sub-laser pulse 101 has a longer transmission distance so as to show a time delay with respect to the sub-laser pulse 102. The sub-laser pulse 101 and the sub-laser pulse 102 are superimposed to eventually provide the laser pulse 104 illustrated in the drawing. Due to constraints imposed by the specifications of the operation machines, the four reflectors 300 shown in FIG. 1 are all fixed in position, which is not adjustable, so that the laser pulse 104 that is finally formed is fixed, making it not possible to further improve the process and result of crystallization of poly-silicon.